This invention relates to improvement of a drive force control system for an infinite speed ratio continuously variable transmission of vehicle.
A belt or toroidal continuously variable transmission for vehicle is known. Also known is an infinite speed ratio continuously variable transmission where, to further enlarge the speed change range of the transmission, the continuously variable transmission is combined with a fixed speed ratio transmission and a planetary gear set so that the speed ratio can be varied infinitely, as disclosed for example in Tokkai Hei 10-267117 published by the Japanese Pat. Office in 1998.
However, in the aforesaid infinite speed ratio continuously variable transmission, the unit input shaft was directly joined to the engine. When a power circulation mode clutch is engaged to begin torque transmission when the vehicle starts, the transmitted torque increases and the engine load increases, while at the same time, the engine rotation speed which was under an idle speed control temporarily increases sharply as shown by the dotted line in FIG. 7. However, in cases where the rotation speed feedback cannot keep up under the idle speed control, the engine stalls.
To avoid the engine stalling, a continuously variable transmission may also be controlled so that the transmitted torque of the infinite speed ratio continuously variable transmission increases gradually, but in this case, the appearance of the drive force was delayed, and the vehicle could not start promptly.
It is therefore an object of this invention, which was conceived in view of the above problems, to avoid an engine stall or racing when a vehicle starts in an infinite speed ratio continuously variable transmission, while at the same time allowing rapid appearance of drive force so that the vehicle can start promptly. Here racing means the rapid engine speed rise which driver does not expect.
In order to achieve the above objects, this invention provides a drive force control system for such a vehicle that comprises an engine, a continuously variable transmission, a fixed speed ratio transmission, a planetary gear set and a selector lever. The continuously variable transmission has a first output shaft to which the rotation of the engine is transmitted at an arbitrary speed ratio. The fixed speed ratio transmission has a second output shaft to which the rotation of the engine is transmitted at fixed speed ratio. The planetary gear set has a first rotation element joined to the first output shaft, a second rotation element joined to the second output shaft, and a third rotation element which varies a rotation direction and a rotation speed according to a difference between a rotation speed of the first rotation element and a rotation speed of the second rotation element. The vehicle runs according to the rotation of the third rotation element.
The drive force control system comprises a sensor which detects the operating range, a first mechanism which increases an output torque of the engine, a second mechanism which increases a torque transmitted by the continuously variable transmission, and a microprocessor. The microprocessor is programmed to determine if the engine rotation speed is equal to a predetermined idle rotation speed, determine if the operating range has changed over from the non-travel range to the travel range, control the first mechanism to increase the output torque of the engine and control the second mechanism to increase the torque transmitted by the continuously variable transmission, when the operating range has changed over from the non-travel range to the travel range.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.